Digital three-dimensional object manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional object printing is an additive process in which successive layers of material are formed on a substrate in different shapes, and is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling. The layers can be formed by ejecting binder material, directed energy deposition, extruding material, ejecting material, fusing powder beds, laminating sheets, or exposing liquid photopolymer material to a curing radiation.
In one or more of these methods, ejector heads are used. Typically, ejector heads, which are similar to printheads in document printers, include an array of ejectors that are coupled to a supply of material. Ejectors within a single ejector head can be coupled to different sources of material or each ejector head can be coupled to different sources of material to enable all or some of the ejectors in an ejector head to eject drops of the same material. Materials that become part of the object being produced are called build materials, while materials that are used to provide structural support during object formation, but are later removed from the object, are known as support materials. Generally, both build materials and support materials are ejected during the formation of each layer to form build portions of a three-dimensional object with build material and form support portions with the support material that support the build portions.
The substrate on which the layers are formed is generally referred to as a build platen. At least one of the build platen and the material deposition devices of the printer are connected to actuators for controlled movement to produce the layers that form the object. Preferably, the object is supported by the build platen during the printing process to facilitate an accurate print, and is removable from the build platen after the conclusion of the printing process without a risk of damaging the object. Conventional techniques, however, generally pose a risk of warping the object during printing and difficulty may be encountered when the object is removed from the build platen.
During the printing process, the build material and support material generally harden in response to cooling, curing, or a similar process. When different portions of a printed object harden at different rates because different materials are used or the portions have different shapes, the object can warp and become distorted. An example of a warped three-dimensionally printed object 10 on a build platen 20 is illustrated in FIG. 9.
One technique used to address this warping issue is to have the object at least partially adhere to the surface of the build platen during printing. The adhered portions of the object are held in place on the surface of the build platen so that the shape of the object is maintained during the printing process and during hardening. A disadvantage of this technique, however, is that removing the adhered portions of the object from the surface of the build platen can be difficult. In particular, when portions of the object formed with build material directly adhere to the build platen, removing the object mechanically can pose a risk of damaging the object.
Techniques have been developed that attempt to address these issues. In one example, build platens have been developed that include heating elements which can be operated in order to heat a base portion of the object to soften the build and support material and facilitate removal from the build platen. Such heaters not only add time to the build process, but also add expense and complexity to the build platen. Additionally, the local heating from the heater can introduce new risks of warping the completed object.
In another example, a base layer of support material is formed prior to depositing the layers of build and support material to form the object. Because the base layer of support material is disposed between the build platen and any portions of the object formed with build material, no build material portions of the object adhere to the build platen. Additionally, support material is generally easier to remove from a substrate than build material. A disadvantage of this technique, however, is that support material generally forms weak adherence to surrounding surfaces, and does not provide sufficient resistance against warping. FIG. 10 illustrates an example of a three-dimensionally printed object 10 that includes a base layer of support material 22 between the layers forming the object 24 and the build platen 20, and is nevertheless warped. FIG. 11 illustrates another example of a warped three-dimensionally printed object 00 that is similar to the object 10 in FIG. 10 but additionally includes a further base layer of build material 32 disposed between the base layer of support material 22 and the build platen 20.
In a further technique, build platens have been developed that define a surface having a plurality of cavities. During the build process, an initial layer of material fills in the cavities in the build platen, and the portions of material within the cavities anchor the object onto the surface of the build platen during printing. In one example of this technique, the initial layer includes a bottom layer of build material of the object being printed. As a result, at least a portion of the printed object includes protrusions that were not part of the original design of the object. Such protrusions generally at least partially adhere to the cavities, and can increase the difficulty of removing the object from the build platen. The protrusions are also a contiguous part of the released object but are not part of the original design. Removing the protrusions in order to achieve an object with the original design can be difficult, and may require additional cleaning such as sanding, cutting, or the like.
In another example, a platen formed from a destructible material such as corrugated cardboard is used, and the initial layer is formed from support material. In order to compensate for the generally weaker strength of the support material, the cavities have a narrowed neck portion so as to form mushroom-like portions of support material within the build platen that locks the object in place with a form fit. As a result of the form fit, removing the object from the build platen requires destroying the platen. In addition to requiring that the platen is replaced for each printing operation, the destructible material that forms the platen may limit materials that can be used as build material and support material.
Therefore, a technique for forming three-dimensional objects that resists warping, that facilitates removal from the build platen, and that does not rely on expensive or complex build platens would be beneficial.